All-optical wavelength division multiplexing (WDM) networks comprise fiber links and all-optical cross-connects to route light paths in the optical domain. All-optical cross-connects are also referred to as photonic cross-connects. They are of different kinds according to their architecture, their components, and their capabilities. After optical space switches, wavelength-selective cross-connects form the next simplest class of optical cross-connects. They are built with wavelength filtering and space switching elements. These elements are often organized in parallel switching planes, where each plane is dedicated to switching channels with a given wavelength.
Referring to FIG. 1, there is shown a wavelength-selective optical cross-connect 10 comprising a plurality of optical demultiplexers 12, a plurality of space switches 14, and a plurality of optical multiplexers 16. In any of the plurality of space switches 14, the crossing of channels with the same frequency produces in-band cross-talk, which is quite detrimental to signal quality.
To minimize in-band cross-talk, wavelength-selective cross-connects are wavelength-dilated. That is, they are instead organized as parallel planes of space switches, where each plane is assigned a set of channels with distinct frequencies sufficiently far apart. Wavelength-dilation ensures that no two channels with identical or close frequencies share the same space switch. Referring to FIG. 2, there is shown a wavelength-dilated wavelength-selective optical cross-connect 20 comprising a plurality of optical demultiplexers 22, a plurality of space switches 24, and a plurality of optical multiplexers 26.
Wavelength-interchanging cross-connects are capable of wavelength conversion. Because of the importance of wavelength conversion, wavelength-interchanging cross-connects form an important class of wavelength-switching optical cross-connects. Wavelength-interchanging cross-connects are built with space switches, wavelength filters, optical amplifiers, and frequency converters based on non-linear optical elements. Some frequency converters are based on wave-mixing, where one or several signals at distinct carrier frequencies mix with a high power pump wave and are frequency-shifted. With wave-mixing, an input signal at frequency f is shifted to frequency (n−1)fP−f, wherein n=2,3 is the order of the wave-mixing process, and fP is the frequency of the pump wave. A constant number of connected wave-mixing devices provide other forms of wave-mixing frequency conversions, such as wave-mixing frequency translations, where an incoming signal at frequency f is shifted to frequency Δ+f, and Δ is a frequency-independent frequency shift. Frequency converters based on wave-mixing can simultaneously process several input signals at distinct frequencies, due to the unique property of bulk frequency conversion. In wavelength-switching cross-connects, wave-mixing devices may also find other uses apart from wavelength conversion, such as chromatic dispersion compensation through phase conjugation, or ultra broadband optical parametric amplification.
Wavelength-switching cross-connects including space switches, wavelength filters, and wave-mixing devices are called wave-mixing cross-connects. Wave-mixing wavelength-interchanging cross-connects are a special class of wavelength-interchanging cross-connects providing wavelength conversion through wave-mixing. Wave-mixing wavelength-interchanging cross-connects are also called parametric wavelength-interchanging cross-connects. Through the bulk frequency conversion property, wave-mixing wavelength-interchanging cross-connects could provide wavelength conversion with a reduced number of converters, compared to previous designs based on dedicated converters. In wave-mixing wavelength-interchanging cross-connects, a large number of channels may share a given wave-mixing frequency converter. However, to avoid in-band cross-talk, no two channels with the same frequency can share the same wave-mixing device.
In all-optical wavelength-switching networks, transmission impairments severely limit the fiber bandwidth available to the C and S bands, both covering a few tens of nanometers. However, in optical cross-connects, there are fewer impairments with technologies such as free space optics. For this reason, optical switching bandwidths may exceed the optical transmission capacity by many orders of magnitude (i.e. a bandwidth mismatch may occur between the transmission and switching capacities). A similar effect occurs with electronic packet switching, where it is possible to design routers running at rates well above line rates. In the electronic domain, this bandwidth mismatch is called speedup and is used to facilitate packet switching. However, in the optical domain, this bandwidth mismatch has yet to be utilized to analogously facilitate photonic wavelength-switching.
In view of the foregoing, it would be desirable to utilize the bandwidth mismatch that occurs between the transmission and switching capacities in an optical system so as to facilitate photonic wavelength-switching.